The present invention relates to an optical resonator for laser oscillating apparatus, and in more detail, to an optical resonator whose optical axis remains substantially unchanged even when the light path of the laser beam is distorted due to temperature change or the like in the lasing gas medium, and moreover, permits to obtain a polarized laser beam.
In recent years, various attempts have been given in order to obtain a laser oscillating apparatus which is small in size and has a high output power.
As one such oscillating apparatus, there exists one in which the optical resonator is composed of a primary mirror, an output mirror, and an appropriate number of folding mirrors.
In this device it is attempted to reduce the length of the resonating cavity by multiply folding a laser beam that travels back and forth between a primary mirror and an output mirror by means of the folding mirrors that are placed to intervene the beam path, so as to let the laser beam pass through the lasing gas medium for many times.
An exmaple of such a structure is, for example, to place a relatively large front folding mirror at one end of the lasing gas medium, to arrange a somewhat small primary mirror and a semi-transmissive output mirror in the vicinity of the front folding mirror, and to arrange a rear folding mirror at the other end of the lasing gas medium so as to oppose the front folding mirror and others. Such as optical resonator is disclosed in Applicant's co-pending application Ser. No. 741,756, filed June 6, 1985, "for Gas Laser Having Thermally Stable Optical Mount."
In this optical resonator, a ray of radiation which is reflected by the primary mirror on one end of the lasing gas medium passes through the lasing gas medium to reach the rear folding mirror on the other side. After being reflected from the rear folding mirror, the ray reaches the front folding mirror on the first end via again the lasing gas medium. Thereafter, the ray is reflected many times between the front folding mirror and the rear folding mirror, and eventually reaches the output mirror on the first end from the rear folding mirror on the other end of the lasing gas medium.
According to the optical resonator, there are formed multiple light paths between the front folding mirror and the rear folding mirror, to give an effective light path which is several times the length of the optical resonator. This then permits to realize a laser oscillating apparatus of small size and high output power.
Now, in a laser oscillating apparatus of the above kind, there was a problem that when a nonuniformity in the spatial distribution of temperature in the lasing gas medium is produced due to supply of energy by a pumping drive, the light path of the laser beam is distorted, resulting in a situation in which it is not possible to output a predetermined laser beam.
Furthermore, when a polarized beam is desired for use, for example, in high precision laser processings, there was a problem in that it is required to insert a special light polarizing means in the optical resonator.